Ultra high frequency antenna system



Filed June 30, 1939 2 Sheets-:Sheet l UPPER NOB 771 LOWEB ZE/ rmq/vamxrm April 15, 1941. e. H. BROWN EIAL.

ULTRA HIGH FREQUENCY ANTENNA SYSTEM Filed June 30, 1939 2 Sheets-Sheet 2 2w .F ML m? B 0 i fi f w a w 7 mm 2 J mm 0 yaw #67 0 P52 V FW; w i U n a Z a H/ m 4% i; u. i r /J a W .mw W Z r 3 w W m WM 5 :2 /a W m fiw My? 5 w i i fi% w r\ Ill 1 u wflm I wflw w w ,0 w

Patented Apr. 15, 1941 UNITED STATES PATENT OFFICE ULTRA HIGH FREQUENCY ANTENNA SYSTEM Application June 30, 1939, Serial No. 282,284

5 Claims.

This invention relates to an ultra high frequency antenna system and has for its principal object the provision of an improved antenna system which combines structural rigidity with a substantially uniform radiation pattern, and which is adapted to be installed on high buildings, or the like, to provide a maximum range of transmission.

The use of a plurality of antennas to provide increased radiation, or to control th radiation pattern, has been suggested previously. In order to obtain the maximum range of radiation at ultra high frequencies it is desirable to mount the antennaswell above surrounding objects. At the same time, however, it is necessary to provide a system in which the effect of the supporting structure on the radiation pattern, if not neutralized, is taken into consideration in providing the desired radiation characteristic, It is therefore a further object of this invention to provide a horizontally or vertically polarized antenna system comprising a plurality of dipole antennas in which the metallic surface of the supporting structure not only shields the antennas from each other but directs the radiation outwardly so as to provide the desired radiation characteristic. A further object of this invention is to provide as improved dipole antenna structure which has sufficient physical rigidity to withstand high wind velocities, and which is further provided with means for preventing accumulations of ice and sleet which would be dangerous not only to the antenna structure itself but to persons and objects below if a sufficiently large formation should occur and become dislodged from the antenna.

This invention will be better understood from the following description when considered in connection with the accompanying drawings in which Figure 1 is a schematic drawing, partly in cross section, illustrating the general arrangement of an antenna system built in accordance with this invention; Figure 2 is a plan view and Figure 3 is an elevation illustrating an antenna arrangement in accordance with this invention; Figure 4 is a view showing the constructural details of a dipole antenna; and Figure 5 is a sectional view of a transmission line utilized in connection with the antenna illustrated in Figure 4; and Figure 6 is a view of a section of one antenna transmission line illustrating the inductive and capacitive correcting section-s.

In accordance with our invention a plurality of dipole antennas are mounted in a horizontal or vertical plane parallel to and substantially a quarter wave length from the respective faces of a supporting structure, which may be the tower of a high building, or the like. In order to increase the radiation in the direction of the horizon we have found that a second similar antenna system may be utilized. The second system is located approximately a half wave length below the first, and consists of identical dipole antennas similarly connected.

Referring to Fig. 1, a system comprising upper and lower groups of horizontal dipole antennas graphically illustrated. The upper group comprises four dipole antennas 1, 9, II and I3 which are preferably mounted opposite the four faces of the supporting structure, as is indicated by the north, east, "south and. west designations. The lower group comprises four similar dipole antennas i5, ll, [9 and 2| which are parallel to the respective antennas oi the upper group.

The various antennas are energized by a trans mitter 23 which is connected to the various antennas through an appropriate transmission line network which consists of concentric line conductors by means of which each arm or element of each dipole antenna is coupled to the transmitter. In order to avoid confusion, in Figure 1 a single line has been used to indicate each concentric transmission line. The terminal ends of the lines, however, have been drawn in greater detail to illustrate the inner and outer conduc tors. Rectangles 30 indicate impedance correcting sections which are connected to each transmission line, and which are illustrated in greater detail in Figs. 4 and 6.

Parallel connections are made between transmission lines which are connected to corresponding elements. By the term corresponding elements as herein used in the specification and claims is meant the elements of each dipole antenna which extend in the same direction from the center of the dipole when viewed facing each antenna from within the supporting structure. Thus, all horizontal dipole elements which point in a clockwise direction are corresponding elements, as are thos pointing counterclockwise. In the case of vertical dipoles all upwardly extending elements are corresponding elements as are all downwardly extending elements. Suitable coupling transformers are utilized to provide an impedance match between the parallel lines and the transmitter output impedance. Thus, element 25 of the upper north dipole I is connected to the corresponding element 29 of the upper east dipole 9 by a concentric line 33, while the other corresponding elements 21 and 3| respectively are also connected together by a transmission line 35. Transmission lines 33 and 35 are connected, respectively, to coupling transformers 31 and 39 by means of transmission lines 34 and 33. The upper south and upper west dipole antennas have corresponding elements connected in parallel in like manner and are also connected to coupling transformers 31 and 39 by means of two transmission lines AI and 43 respectively. The antennas of the lower group are connected in a similar manner, corresponding elements 49, 5| of the lower north and east antennas being connected to coupling transformer 39 by a transmission line 35, while the remaining elements 53,

are connected to coupling transformer 31 through a transmission line 41. The south and west antennas of the lower group are connected in like manner to the coupling transformers by.

established between the open end of the central conductor and the drum. The ratio of the inner diameter of the drum 6| to the outer diameter of conductor 93 is preferably as large as possible, sothat the impedance at the resonant frequency is likewise large, and the change of impedance for frequencies on either side of resonance is minimizd. The ratio of the inner diameter of the central conductor 63 to the outer diameter of conductor 65 is selected to provide a proper impedance to match the impedance of the antenna transmission lines. We have found this value to be of the order of 72 ohms.

The connection of the transmission lines Within the coupling transformers is made so that a proper phase relation in the various antenna elements is established. The arrowheads on the antenna elements and transmission lines indicate the instantaneous current flow in the system. Thus, transmission lines 59 and 41 are connected in parallel within the coupling transformer 31, and are connected to the inner conductor 65. Transmission lines 4i and 34 are connected in parallel Within coupling transformer 31, and are also connected to the open end of the central conductor 63. The currents in the first two transmission lines are, therefore, of a given phase, while the currents in the last-named transmission lines are in phase opposition thereto. Coupling transformer 39 is similarly connected to the transmission lines. Thus, transmission lines 36 and 43 are connected to the open end of the central conductor 61, while transmission lines 51 and 45, are connected to the inner conductor 69.

A third coupling transformer H is provided to connect the transmitter 23-to the two coupling transformers 31 and 39, and to provide a suitable impedance match. Transformer H is similar to the other transformers and is provided with two output transmission lines '13 and 15 which are connected respectively to the coupling transformers 31 and 39. It will be noted that the currents feeding the two last-named coupling transformers are in phase opposition, and conse'quently that the currents in the output transmission lines which are connected to the respective inner conductors 65 and 99 are likewise in phase opposition.

The physical arrangement of the antennas on a supporting structure is best illustrated by reference to Figures 2 and 3. The dipole antennas 1, 9, etc., are arranged parallel to the four faces of a building 11 and are placed so as to produce horizontally polarized radiations, although, if desired, the dipole antennas may be positioned vertically to produce vertically polarized radiations. The radiating elements of the antennas are spaced approximately a quarter wave length from the adjacent face of the building. By providing a metallic facing on the four sides of the building, the radiating energy from one antenna is effectively prevented from reaching the other antennas and is reflected outwardly from the building surface. The resultant radiation pattern is substantially uniform, although there is a tendency for the pattern to assume a somewhat rectangular shape.

The actual physical construction of one of the dipole antennas is illustrated in Figs. 4 and 5. A unique arrangement is illustrated in which the radiating elements 19 and 8| are rigidly supported by the two tubular outer conductors 83 and 85 of the transmission lines. The outer conductors 83 and 85 terminate at their outer end at an end plate 91, which is provided with two openings through which the inner conductors 39 and 9| are passed. A suitable cap 93 is securely fastened to the end plate 81. Radiating elements 19 and SI- are mounted by means of suitable insulators 95 and 91 on opposite faces of the cap 93. Connections are made within the cap between the radiating elements and the inner conductors of the transmission lines. This may be accomplished by means of junction blocks 99 and I01, which are suitably drilled, or are provided with clamps to receive the respective conducting elements.

Conductors 83 and 85 are brought through the building wall H3 and securely fastened thereto in any suitable fashion. Within the building and approximately a quarter wave length from the wall two correcting networks H5 and H1 are connected to the two lines. Each network comprises an inductive and a capacitive correcting section, the construction and operation of which will be described hereinafter.

To avoid ice formations on the antenna structure, provision has been made for applying heat to the entire structure. Small hollow tubes I03 and W5 are mounted on and are parallel to tubes 33 and 85, .and heating elements I94, I09 are placed within the small tubes. The heating elements are likewise extended within the two radiating elements 19 and BI which are made hollow to receive the heating elements. Suitable insulating bushings are provided where necessary to prevent the heating elements from shortcircuiting to the hollow tubes I93, I 05, or the antenna elements 19, BI. However, the heating elements are electrically connected to the outer ends of the radiating elements, at points I91, I09, so that the antenna itself provides the return path for the heating currents. The heating elements are connected to any suitable source of heating current, such as a generator III. Inorder to provide the maximum heating efficiency, the hollow tubes I93, I05 containing the heating elements are preferably mounted beneath the transmission line conductors. Ashorting-bar 86 is slidably mounted on the hollow tubes I03, I05.

The position of this bar is adjusted to tune the outer portion of the tubes to quarter wave resonance. The heating tubes are clamped to the transmission line conductors at this point, which is a voltage minimum, by a pair of clamps 90, 92.

We have found that the metallic cap 93 adds a certain amount of lumped capacitance to the transmission line and antenna elements, largely due to the capacity of junction blocks 99 and HM. In order to provide compensation and to adjust the electrical resonant characteristics of the antenna, the inner conductors 89 and 9| of the transmission line which is used to support the antenna may be made in sections of different diameters, as illustrated in Fig. 5. The first quarter wave section, for example, has a diameter which provides an impedance match to the antenna impedance. The next quarter wave section 89a of the inner conductor has a diameter somewhat less than the diameter of the preceding section. In addition, the length of this section is slightly less than a quarter wave so as to provide an inductive reac-tance which compensates for the excessive capacitive reactance of the antenna itself.

, If the antenna arrangement illustrated is to be used for the transmisison or reception of speech its impedance will be sufficiently uniform through the range of side-band frequencies. However, where television video signals are to be transmitted it is advisable to provide a correcting network which has an impedance versus frequency characteristic suitable to provide compensation over the extremely wide range of side-band frequencies which are utilized. To illustrate a preferred embodiment of such a correcting network reference is now made to Figs. 4 and 6.

To each transmission line two correcting sections are connected. One of the correcting sections H5, is inductive and the other, H9, is capacitive and the two are adjusted to parallel resonance at the operating frequency. The sections comprise inner, l2l, and I23, and outer, I25 and I21, concentric conductors which are respectively connected to the inner and outer conductors of the antenna transmission line, as shown in Fig. 6.

A shorting plug I29, which is slidably mounted within each inductive section, is arranged to short circuit the inner and outer conductors. The inner conductor of each capacitive section terminates in a plate l3! which is in capacitive relation to an adjustable plug I33. By adjusting the positions of the plugs the correcting sections of each transmission line may be tuned to parallel resonance, and may be given any desired inductance-capacity ratio. This ratio determines the slope of the impedance versus frequency characteristic so that the characteristic of the line, looking toward the antenna, may be compensated by a reciprocal characteristic of the shunt-connected correcting sections.

, While Fig. 1 represents the preferred arrangements, it is possible to eliminate the upper or lower group of dipole antennas and utilize one antenna opposite each face of the building.

Since, as we have pointed out above, the addition of the lower group of antennas increases radiation in the direction of the horizon, the ar rangement illustrated is preferred, although the system may be simplified by the suggested modification. If such a modification is made, one of the coupling transformers 31 and 39 may be eliminated, as well as the coupling transformer H. In such a case, the transmission lines from the antennas will be connected to the same coupling transformer, it being necessary only to ascertain that the proper phase relationships are maintained.

We have thus described an antenna system which is suitable for use at ultra high frequencies and which provides substantially uniform radiation, and therefore overcomes one of the inherent disadvantages of the dipole antenna, which may be utilized to provide either horizontally or vertically polarized radiation, and which takes advantage of the reflecting surface provided by a supporting structure such as a building, or the like.

We claim as our invention:

1. An ultra high frequency antenna system comprising a supporting structure having a plurality of angularly disposed faces, a plurality of dipole antennas each having coaxially extending radiating elements, at least one of said antenas being adjacent and substantially parallel to each face of said supporting structure, and means for producing in phase currents in corresponding elements of said dipole antennas, said structure faces being adapted to reflect energy radiated from said elements and being of sufficient area to shield the antenna adjacent one face from antennas adjacent the other faces so that a substantially uniform radiation pattern in a horizontal plane is thereby produced.

2. An ultra high frequency antenna system comprising a supporting structure having a plurality of angularly disposed faces, a plurality of horizontal dipole antennas each having coaxially extending radiating elements, at least one of said antennas being adjacent and substantially parallel to each face of said supporting structure, and means for producing in phase currents in corresponding elements of said dipole antennas, said structure faces being adapted to reflect energy radiated from said elements and being of sufficient area to shield the antenna adjacent one face from antennas adjacent the other faces so that a substantially uniform radiation pattern in a horizontal plane is thereby produced.

3. An ultra high frequency antenna system comprising a supporting structure having four angularly disposed faces, four dipole antennas each having coaxially extending radiating elements, one of said antennas being adjacent and substantially parallel to each face of said supporting structure, and means for producing in phase currents in corresponding elements of said dipole antennas, said structure faces being adapted to reflect energy radiated from said elements and being of sufficient area to shield the antenna adjacent one face from antennas adjacent the other faces so that a substantially uniform radiation pattern in a horizontal plane is thereby produced.

4. An ultra high frequency antenna system comprising a supporting structure having a plurality of angularly disposed faces, a plurality of dipole antennas each having coaxially extending radiating elements, at least one of said antennas being mounted a quarter wavelength from and substantially parallel to each face of said supporting structure, and means for producing in phase currents in corresponding elements of said dipole antennas, said structure faces being adapted to reflect energy radiated from said elements and being of sufiicient area to shield the antenna adjacent one face from antennas adjacent the other faces so that a substantially uniform radiation pattern in a horizontal plane is thereby produced.

5. An ultra high frequency antenna system comprising a supporting structure having a plurality of angularly disposed vertical faces, a plurality of horizontal dipole antennas each having coaxially extending radiating elements, at least one of said antennas being adjacent and substantially parallel to each face of said supporting structure, and means for producing in phase currents in corresponding elements of said dipole antennas, said structure faces being adapted to reflect energy radiated from said elements and being of sufiicient area to shield the antenna adjacent one face from antennas adjacent the other faces so that a substantially uniform radiation pattern in a horizontal plane is thereby produced.

GEORGE H. BROWN.

ROBERT F. LEWIS. 

